Merge the Merlin heap tracing to top-of-trunk.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 6609958e5cee8f4256c9f327806cf355cf3c4e1a..7cf15ce0f4d510c07e8f8caa89cfdf1c4c5b3fa9 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -719,7 +719,7 @@ DART_EXPORT Dart_Handle Dart_RemoveGcEpilogueCallback(
 }
 
 
-DART_EXPORT Dart_Handle Dart_HeapProfile(Dart_HeapProfileWriteCallback callback,
+DART_EXPORT Dart_Handle Dart_HeapProfile(Dart_FileWriteCallback callback,
                                          void* stream) {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
@@ -4411,6 +4411,14 @@ DART_EXPORT void Dart_GetPprofSymbolInfo(void** buffer, int* buffer_size) {
 }
 
 
+DART_EXPORT void Dart_InitHeapTrace(Dart_FileOpenCallback open_function,
+                                    Dart_FileWriteCallback write_function,
+                                    Dart_FileCloseCallback close_function,
+                                    const char* prefix) {
+  HeapTrace::InitTracing(open_function, write_function, close_function, prefix);
+}
+
+
 DART_EXPORT void Dart_InitPerfEventsSupport(Dart_FileWriterFunction function) {
   Dart::set_perf_events_writer(function);
 }